This invention relates to a method of producing welded joint including a non-welded portion, and more particularly to such a method of increasing strengths of the joint concerning the fatigue fracture and brittle fracture.
The term "joint" used herein and in the appended claims means a portion joining a member to another member.
In general, welded joints including the non-welded portion such as cross joints, T joints etc. are most frequently employed because of their convenience. However, it is well known that such welded joints have much lower fatigue strength than flat mother materials thereof. This has resulted in the restriction that those joints can not be employed in important constructions to which loads are repeatedly applied. The reasons for which welded joints including the non-welded portion are low in fatigue strength have been heretofore investigated by utilizing fracture mechanics. This low fatigue strength has been attributed to the fact that sharp notches are formed at the extremities of the non-welded portion and can be large enough to cause spontaneous sharp cracks such as fissures, fatigue cracks etc. Those sharp notches cause the concentration of high stress.
In order to increase the fatigue strength of those welded joints, it has been previously proposed to dispose the large groove on conventional joints to form welded joints with full penetration. This measure has been disadvantageous in that, with the welding desired to be effected in a narrow area, it is difficult to perform the welding operation. Also, even though the welding operation could be performed, the particular amount of deposit metal is redoubled, resulting in a great reduction in efficiency and/or occurrence of high welding distortion.
Accordingly it is an object of the present invention to decrease the concentration of stress on a root portion of a welded joint including a non-welded portion to increase its strengths concerning the fatigue fracture and brittle fracture.
It is another object of the present invention to substantially eliminate or minimize the disadvantages of conventional welded joints with the full penetration fillet including no non-welded portion; such as the redoubling of an amount of deposit metal and the occurrence of high welding distortion.